Michael Pappas reported in bug #47805:
I have a 64-bit windows 7 box, on which I just installed 3.5.3. In 32-bit
Windows 7, under Control Panel -> Indexing Options -> Advanced -> File Types
one can see that C:\Program Files (x86)\LibreOffice
3.5\program\shlxthdl\ooofilt.dll is associated for LibO files.
On my own 64-bit system, "No registered IFilter was found" is displayed. I have
tried your regsvr commands*, thinking that they will solve this issue, but after
a reboot I still see the same message there...
* regsvr32 "C:\Program Files (x86)\LibreOffice 3.5\program\shlxthdl\ooofilt_x64.dll"